Electric drive device and electric power steering device

ABSTRACT

An electric drive device has a motor housing accommodating an electric motor, a heat radiation base body fixed to an end surface, which is opposite side to an output shaft portion of a motor rotation shaft, of the motor housing and extending in a rotation shaft direction that is opposite side to output shaft portion, one electronic control unit of redundant system, arranged along direction in which heat radiation base body extends and having board, fixed to the heat radiation base body with thermal conduction to heat the radiation base body allowed, and the other electronic control unit of redundant system, arranged along direction in which the heat radiation base body extends and having a board, fixed to the heat radiation base body with thermal conduction to heat radiation base body allowed. Boards of both electronic control units are fixed to the heat radiation base body with boards slanting with respect to an extension direction of the heat radiation base body.

TECHNICAL FIELD

The present invention relates to an electric drive device and anelectric power steering device, and more particularly to an electricdrive device and an electric power steering device in which anelectronic control unit is mounted.

BACKGROUND ART

In a field of general industrial equipment, a mechanical control elementis driven by an electric motor. In recent years, so-called electricallymechanically integrated electric drive device, which is configured suchthat an electronic control unit formed from a semiconductor element etc.controlling a rotation speed and/or a rotation torque of the electricmotor is integrally mounted in the electric motor, has been used.

As an example of the electrically mechanically integrated electric drivedevice, for instance, an electric power steering device is configuredsuch that a turning direction and a turning torque of a steering shaftthat turns by driver's operation of a steering wheel are detected, andon the basis of these detection values, the electric motor is driven soas to rotate in the same direction as the turning direction of thesteering shaft, then a steering assist torque is generated. To controlthis electric motor, the power steering device is provided with anelectronic control unit (ECU: Electronic Control Unit).

As a related art electric power steering device, for instance, anelectric power steering device disclosed in Japanese Unexamined PatentApplication Publication No. 2013-060119 (Patent Document 1) is known.Patent Document 1 discloses the electric power steering deviceconfigured by an electric motor unit and an electronic control unit. Anelectric motor of the electric motor unit is housed in a motor housinghaving a cylindrical portion that is made of aluminum alloy etc. Boards(substrates) on which electronic elements or components of theelectronic control unit are mounted are housed in an ECU housing that islocated on an opposite side to an output shaft of the motor housing inan axial direction of the motor housing. The boards housed in the ECUhousing are provided with a power supply circuit unit, a powerconversion circuit unit having a power switching element such as aMOSFET and an IGBT that drive and control the electric motor, and acontrol circuit unit that controls the power switching element. Outputterminals of the power switching element and input terminals of theelectric motor are electrically connected through a bus bar.

Power is supplied to the electronic control unit housed in the ECUhousing from a power supply through a connector terminal assembly madeof synthetic resin. Further, detection signals concerning an operatingstate etc. are sent to the electronic control unit from detectionsensors. The connector terminal assembly functions as a lid member or acover member, and is connected to the electronic control unit so as tocover an opening formed at the ECU housing. The connector terminalassembly is fixed to an outer surface of the ECO housing with fixingbolts.

As another electric drive device configured such that the electroniccontrol unit and the electric motor unit are integrated, electric brakeand an electric hydraulic pressure controller for a various kinds ofhydraulic pressure control are known.

CITATION LIST Patent Document

Patent Document 1: Japanese Unexamined Patent Application PublicationNo. 2013-060119

SUMMARY OF THE INVENTION Technical Problem

Since the electric power steering device disclosed in Patent Document 1is placed in an engine room of the vehicle, size reduction inconfiguration of the electric power steering device is required. Inparticular, there has been a tendency in recent years for variousauxiliary devices such as an exhaust gas control device and a safetyprecaution device to be disposed in the engine room of the vehicle. Itis therefore required for the auxiliary devices including the electricpower steering device to be as small as possible. Further, reduction incomponent count of the auxiliary devices including the electric powersteering device is required.

In the electric power steering device having a configuration disclosedin Patent Document 1, the power supply circuit unit, the powerconversion circuit unit and the control circuit unit are mounted on twoboards that are arranged in a radial direction. For this reason, sincecomponent count of electrical component required to control the electricmotor is roughly determined, when these electrical components aremounted on the two boards, size of the ECU housing accommodating thereinthe electronic control unit necessarily increases in the radialdirection.

Further, safety is particularly required of the electric power steeringdevice to steer the vehicle, and an electronic control unit having aredundant system such as a dual-redundancy system is required.Therefore, two systems of the electronic control unit, which are thesame as each other, are necessary as a configuration of the redundantsystem. Also from this point of view, there is a tendency for the sizeof the ECU housing to further increase.

Here, from a structural viewpoint, limit of an axial length of theelectric power steering device in a longitudinal direction is notstrict, but there is a tendency to limit increase in size of theelectric power steering device in the radial direction. Hence, underpresent circumstances, size reduction of the electric drive device inthe radial direction is required.

In addition to this, the electrical component forming the power supplycircuit unit and the power conversion circuit unit has a large heatvalue. Therefore, when reducing the size of the electric drive device,it is required for this heat to efficiently radiate to the outside.

An object of the present invention is therefore to provide a newelectric drive device and a new electric power steering device which arecapable of suppressing the increase in size in the radial direction ofthe electric drive device formed by the electric motor unit in which theelectronic control unit having the redundant system is integrated, andwhich have a simple heat radiation structure configured by as small thecomponent count as possible.

Solution to Problem

An electric drive device comprises: a motor housing accommodatingtherein an electric motor that drives a mechanical control element; aheat radiation base body fixed to an end surface, which is an oppositeside to an output shaft portion of a rotation shaft of the electricmotor, of the motor housing and extending in a direction of the rotationshaft which is the opposite side to the output shaft portion; oneelectronic control unit of a redundant system, the one electroniccontrol unit arranged along a direction in which the heat radiation basebody extends and having a board that is fixed to the heat radiation basebody with thermal conduction to the heat radiation base body allowed;and the other electronic control unit of the redundant system, the otherelectronic control unit arranged along a direction in which the heatradiation base body extends and having a board that is fixed to the heatradiation base body with thermal conduction to the heat radiation basebody allowed. And, the board of the one electronic control unit and theboard of the other electronic control unit are fixed to the heatradiation base body with the both boards slanting with respect to adirection in which the heat radiation base body extends.

Effects of Invention

According to the present invention, since the board of the electroniccontrol means (the electronic control unit) is set along the heatradiation base body provided in the axial direction, size reduction ofthe electric drive device can be achieved. Further, since the board ofthe electronic control means (the electronic control unit) of theredundant system is fixed to the heat radiation base body with the boardslanting or leaning with respect to a direction in which the heatradiation base body extends, an area of the control circuit board can belarge, thereby rapidly storing or accumulating the heat from theelectronic elements or components to the board. Moreover, since acontact area of the board to the heat radiation base body can be large,rapid removal of the heat from the board to the heat radiation base bodyis secured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general perspective view of a steering device as an exampleto which the present invention is applied.

FIG. 2 is a general perspective view of a related art electric powersteering device.

FIG. 3 is a perspective exploded view of an electric power steeringdevice according to an embodiment of the present invention.

FIG. 4 is a perspective view showing a state in which a positiondetection circuit board is mounted in an electric motor unit.

FIG. 5 is a perspective view of a heat radiation base body secured tothe electric motor unit.

FIG. 6 is a perspective view showing a state in which the heat radiationbase body is mounted on the electric motor unit.

FIG. 7 is a cross section for explaining a fixing way of the electricmotor unit and the heat radiation base body.

FIG. 8 is a perspective view showing a state in which an electroniccontrol means (an electronic control unit) having a redundant system isfixed to the heat radiation base body.

FIG. 9 is a longitudinal cross section of an A-A line of FIG. 8, andexplains a modified example.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will foe explained in detailbelow with reference to the drawings. The present invention is notlimited to the following embodiment, and includes all designmodifications and equivalents belonging to the technical scope of thepresent invention.

Before explaining the embodiment of the present invention, aconfiguration of a steering device as an example to which the presentinvention is applied will be briefly explained using FIG. 1. Further, tofacilitate the understanding of the present invention, a configurationof a related art electric power steering device will also be brieflyexplained using FIG. 2.

First, a steering device to steer front wheels of a vehicle will beexplained. A steering device 1 is configured as shown in FIG. 1. Apinion (not shown) is provided at a lower end of a steering shaft 2connecting to a steering wheel (not shown). This pinion is engaged witha rack (not shown) that extends in right and left directions of avehicle body. A tie rod 3 to steer the front wheels in the right andleft directions is each connected to both ends of the rack. The rack isaccommodated in a rack housing 4. Between the rack housing 4 and eachtie rod 3, a rubber boot 5 is provided.

The steering device 1 is provided with an electric power steering device6 to assist torque when performing a turning operation of the steeringwheel. That is, a torque sensor 7 that detects a turning direction and aturning torque of the steering shaft 2 is provided. And, an electricmotor unit 8 that provides a steering assistive force to the rack via agear 10 on the basis of a detection value of the torque sensor 7 isprovided. Further, an electronic control unit (ECU) 9 that controls anelectric motor disposed in the electric motor unit 8 is provided. Theelectric motor unit 8 of the electric power steering device 6 isconnected to the gear 10 at three portions of an outer periphery at anoutput shaft side of the electric motor unit 8 with bolts (not shown).The electronic control unit 9 is disposed on an opposite side to theoutput shaft side of the electric motor unit 8.

As shown in FIG. 2, the electric motor unit 8 of the related artelectric power steering device is formed from a motor housing 11A havinga cylindrical portion made of aluminum alloy etc. and the electric motor(not shown) disposed in the electric motor unit 8. The electroniccontrol unit S is formed from an ECU housing 11B located on an oppositeside to an output shaft of the motor housing 11A in an axial directionof the motor housing 11A and made of aluminum alloy etc. and anelectronic control assembly (not shown) housed in the ECU housing 11B.

The motor housing 11A and the ECU housing 11B are fixedly connected toeach other on their opposing end surfaces with fixing bolts. Theelectronic control assembly housed in the ECU housing 11B is configuredby a power supply circuit unit that generates a required power, a powerconversion circuit unit having a power switching element formed from aMOSFET or an IGBT that drives and controls the electric motor of theelectric motor unit 8, and a control circuit unit that controls thepower switching element. Output terminals of the power switching elementand input terminals of the electric motor are electrically connectedthrough a bus bar.

A synthetic-resin-made lid member (or cover member) 12, which is alsoused as a connector terminal assembly, is fixed to an end surface of theECU housing 11B with fixing bolts. The lid member 12 is provided with aconnector terminal forming portion 12A for power supply, a connectorterminal forming portion 12B for detection sensors, and a connectorterminal forming portion 12C for control state output by which a controlstate is outputted to an external device. The electronic controlassembly housed in the ECU housing 11B is supplied with power from apower supply through the connector terminal forming portion 12A forpower supply of the synthetic-resin-made lid member 12. Further, theelectronic control assembly is provided with detection signals of anoperating condition etc. from the detection sensors through theconnector terminal forming portion 12B for detection sensors. A currentcontrol state signal of the electric power steering device is outputtedfrom the electronic control assembly through the connector terminalforming portion 12C for control state output.

Here, the lid member 12 is shaped so as to cover an entire opening ofthe ECU housing 11B. However, size of each of the connector terminalscould be reduced, then each connector terminal could be connected to theelectronic control assembly through insertion holes formed at the ECUhousing 11B.

In the electric power steering device 6, when the steering shaft 2 isturned in any turning direction by the steering wheel operation, thetorque sensor 7 detects the turning direction and the turning torque ofthe steering shaft 2. The control circuit unit calculates a driveoperation amount of the electric motor on the basis of these detectionvalues. The electric motor is then driven by the power switching elementof the power conversion circuit unit on the basis of the calculateddrive operation amount. And, an output shaft of the electric motorrotates so as to drive and rotate the steering shaft 2 in the samedirection as a direction of the steering wheel operation. This rotationof the output shaft of the electric motor is transmitted to the rack(not shown) through the pinion (not shown) and the gear 10, and thevehicle is steered. Since such configuration and workings are wellknown, a further explanation will be omitted here.

In such electric power steering device, as mentioned above, there hasbeen a tendency in recent years for various auxiliary devices such asthe exhaust gas control device and the safety precaution device to bedisposed in the engine room of the vehicle. It is therefore required forthe auxiliary devices including the electric power steering device to beas small as possible.

In the electric power steering device having such configuration, thepower supply circuit unit, the power conversion circuit unit and thecontrol circuit unit are mounted on the two boards, and are arranged inthe radial direction so as to be orthogonal to an axis of the ECUhousing. For this reason, since component count of the electricalcomponent required to control the electric motor is roughly determined,when these electrical components are mounted on the two boards, size ofthe ECU housing accommodating therein the electronic control unitnecessarily increases in the radial direction.

Further, safety is particularly required of the electric power steeringdevice to steer the vehicle, and an electronic control unit having aredundant system such as a dual-redundancy system is required.Therefore, two systems of the electronic control unit, which are thesame as each other, are necessary as a configuration to improve theredundant system, and the number of electronic elements or components isthe double. Also from this point of view, the size of the ECU housingfurther increases.

Here, from a structural viewpoint, limit of the axial length of theelectric power steering device in the longitudinal direction is notstrict, but there is a tendency to limit increase in size of theelectric power steering device in the radial direction. Hence, underpresent circumstances, size reduction of the electric drive device inthe radial direction is required. In addition to this, the electricalcomponent forming the power supply circuit unit and the power conversioncircuit unit has a large heat value. Therefore, when reducing the sizeof the electric drive device, it is required for this heat toefficiently radiate to the outside.

From such background, the present embodiment proposes the electric powersteering device having the following configuration.

That is, in the present embodiment, an electric drive device has: amotor housing accommodating therein an electric motor; a heat radiationbase body fixed to an end surface, which is an opposite side to anoutput shaft portion of a rotation shaft of the electric motor, of themotor housing and extending in a direction of the rotation shaft whichis the opposite side to the output shaft portion; one electronic controlunit of a redundant system, the one electronic control unit arrangedalong a direction in which the heat radiation base body extends andhaving a board that is fixed to the heat radiation base body withthermal conduction to the heat radiation base body allowed; and theother electronic control unit of the redundant system, the otherelectronic control unit arranged along a direction in which the heatradiation base body extends and having a board that is fixed to the heatradiation base body with thermal conduction to the heat radiation basebody allowed And, the board of the one electronic control unit and theboard of the other electronic control unit are fixed to the heatradiation base body with the both boards slanting with respect to adirection in which the heat radiation base body extends. Then, heatradiates from the motor housing through the heat radiation base body.

According to the configuration of the present invention, since the boardof the electronic control means (the electronic control unit) is setalong the heat radiation base body provided in the axial direction, sizereduction of the electric drive device can be achieved. Further, sincethe board of the electronic control means (the electronic control unit)of the redundant system is fixed to the heat radiation base body withthe board slanting or leaning with respect to a direction in which theheat radiation base body extends, an area of the control circuit boardcan be large, thereby rapidly storing or accumulating the heat from theelectronic elements or components to the board. Moreover, since acontact area of the board to the heat radiation base body can be large,rapid removal of the heat from the board to the heat radiation base bodyis secured.

In the following description, a configuration of the electric powersteering device according to the embodiment of the present inventionwill be explained in detail with reference to FIGS. 3 to 9. FIG. 3 is adrawing, viewed from an oblique direction, with components of theelectric power steering device of the embodiment dismantled. FIGS. 4 to9 are drawings showing each assembly state of the components of theelectric power steering device when assembled in assembly order. Theexplanation will be made with reference to each drawing as necessary.

FIG. 3 is a perspective exploded view of the electric power steeringdevice 6. An iron-made annular side yoke (not shown) is fitted to aninside of a motor housing 20. The electric motor is accommodated insidethis side yoke. An output shaft portion 21 of the electric motorprovides the steering assistive force to the rack via the gear. Since aspecific structure of the electric motor is well known, its explanationwill be omitted here.

The motor housing 20 is made of aluminum alloy, and acts as a heat sinkthat radiates heat generated at the electric motor and heat generated inelectronic elements or components mounted on after-mentioned electroniccontrol boards to the outside atmosphere. The electric motor and themotor housing 20 form an electric motor unit EM.

An electronic control unit EC is connected to an end surface of themotor housing 20 which is opposite side of the output shaft portion 21of the electric motor unit EM. The electronic control unit EC is formedfrom a position detection circuit board 22, a heat radiation base body23, a first power conversion circuit board 24, a first control circuitboard 25, a second power conversion circuit board 26, a second controlcircuit board 27, and a power supply connector 28.

Here, the first power conversion circuit board 24, the first controlcircuit board 25, the second power conversion circuit board 26 and thesecond control circuit board 27 form a redundant system. A mainelectronic control means (a main electronic control unit) is formed bythe first power conversion circuit board 24 and the first controlcircuit board 25. A sub-electronic control means (a sub-electronic:control unit) is formed by the second power conversion circuit board 26and the second control circuit board 27.

In a normal condition, the electric motor is driven and controlled bythe main electronic control unit. However, if an abnormal condition or afailure occurs to the first power conversion circuit board 24 or thefirst control circuit board 25 of the main electronic control unit, thecontrol is switched to the sub-electronic control unit, and the electricmotor is driven and controlled by the second power conversion circuitboard 26 and the second control circuit board 27 of the sub-electroniccontrol unit.

Therefore, normally, heat from the main electronic control unit istransmitted to the heat radiation base body 23. If the abnormalcondition or the failure occurs to the main electronic control unit, themain electronic control unit stops and the sub-electronic control unitoperates, then heat from the sub-electronic control unit is transmittedto the heat radiation base body 23. These will be described later.

However, both of the main electronic control unit and the sub-electroniccontrol unit could operate as a regular electronic control unit,although the present invention does not apply this configuration. And,if the abnormal condition or the failure occurs to one of the electroniccontrol units, the other electronic control unit drives and controls theelectric motor by half ability. In this case, although capability of theelectric motor is half, so-called limp-home function is secured.Therefore, in the normal condition, heat from the main electroniccontrol unit and the sub-electronic control unit is transmitted to theheat radiation base body 23.

The electronic control unit EC is not housed in the ECO housing of therelated art as shown in FIG. 2. Therefore, heat of the electroniccontrol unit EC does not radiate from the ECU housing. In the presentembodiment, the electronic control unit EC is configured to be securedto and supported by the motor housing 20. And, heat of the electroniccontrol unit EC radiates mainly from the motor housing 20. Whencompleting assembling the electronic control unit EC and the electricmotor unit EM, the electronic control unit EC is covered by a cover 29.The cover 29 and the motor housing 20 are connected to each other withthe cover 29 facing to the end surface of the motor housing 20.

The cover 29 could be made of synthetic resin or metal. The cover 29 isfixedly connected to the motor housing 20 by fixing way or fixing meanssuch as adhesion (adhesive), welding and bolt. In this manner, in thepresent embodiment, in the electric power-steering device, a sealingpart is only a connecting portion between the motor housing 20 and thecover 29. Therefore, an additional structure of the sealing part and asealing component required for the seal can be reduced.

Further, since it is not necessary for the cover 29 to support theelectronic control unit EC, a thickness of the cover 29 can be thin,which contributes to size reduction of the control unit EC in the radialdirection and weight reduction of the control unit EC. If the cover 23is made of metal (e.g. aluminum alloy or iron), the cover 29 has a heatradiation function. Therefore, heat from the motor housing 20 istransmitted to the cover 29, then a heat radiation effect is furtherimproved.

As described above, in the present embodiment, the position detectioncircuit board 22 is fixed to the end surface of the motor housing 20.The first power conversion circuit board 24, the first control circuitboard 25, the second power conversion circuit board 26 and the secondcontrol circuit board 27 are fixed to the heat radiation base body 23with these boards facing to each other. Further, the heat radiation basebody 23 is fixed to the end surface of the motor housing 20 so as tocover the position detection circuit board 22. Furthermore, the cover 29and the motor housing 20 are configured such that the cover 29 isliquid-tightly connected to the end surface of the motor housing 20.This configuration is one of outstanding features of the presentembodiment.

That is, the present embodiment does not require the ECO housing likethe electric power steering device of the related art as shown in FIG.2, which is located on the opposite side to the output shaft of themotor housing in the axial direction of the motor housing and is made ofaluminum alloy etc.

Consequently, the ECU housing like the related art, a seal to secureliquid tightness of the ECU housing and a bolt to fix the motor housingand the ECU housing are not necessary in the present embodiment. It istherefore possible to reduce a whole body size of the electric powersteering device. Further, component count can be reduced, therebyreducing man-hour of assembly or assembly processes. With this, a finalproduct piece rate (or a final product unit price) can be suppressed,and this gives rise to improvement in product-competitiveness.

Returning to FIG. 3, a rotor portion (not shown) of the electric motoris disposed in a middle portion of the motor housing 20. A statorwinding is wound around this rotor portion. The stator winding isconnected by star connection. An input terminal 30 of the winding ofeach phase and a neutral terminal 31 of each phase, for one of theredundant system, protrude from an opening 32 that is formed at themotor housing 20. In the present embodiment, since the redundant systemis configured, for the other of the redundant system, other inputterminal 30 of the winding of each phase and other neutral terminal 31of each phase protrude from an opening 32 formed at the motor housing20. These input terminals 30 and neutral terminals 31 protrude from theopenings 32 with the terminals 30 and 31 for one of the redundant systemand the terminals 30 and 31 for the other of the redundant systemarranged at 180° angular-space.

The input terminal 30 of the winding is connected to an output terminalof the first power conversion circuit board 24 forming the mainelectronic control unit for each phase. The neutral terminal 31 for eachphase is connected to the position detection circuit board 22 through awiring pattern on the wiring board 22, and forms a neutral point.Likewise, for the other of the redundant system, the input terminal 30of the winding is connected to an output terminal of the second powerconversion circuit board 26 forming the sub-electronic control unit foreach phase. Also, for the other of the redundant system, the neutralterminal 31 for each phase is connected to the position detectioncircuit board 22 through the wiring pattern on the wiring board 22, andforms the neutral point. These configurations are basically almost thesame because of the redundant system.

These configurations are also one of the outstanding features of thepresent embodiment. Since the neutral terminals 31 of the mainelectronic control unit and the sub-electronic control unit for eachphase are connected to the position detection circuit board 22 throughthe wiring pattern on the wiring board 22 in this manner, no complicatedwiring route of the neutral terminals 31 is required, then a wiringstructure is extremely simple. In addition, since complicated wiringroute of the input terminals 30 to the respective power conversioncircuit boards 24 and 26 is not required, a space for this complicatedwiring route is also not required. Size reduction of the electroniccontrol unit EC can therefore be achieved. This will be explained usingFIG. 8.

Here, a bearing that supports a rotation shaft forming the rotor portionis provided between the two openings 32 of the motor housing 20,although this is not illustrated in the drawing. A sealing plate 33 isprovided at the end surface side of the motor housing 20 so as to coverthis bearing portion from the outer side. The sealing plate 33 is aplate that shields the rotor portion from the outside, and is providedso that after the cover 29 is fixed, a filler that fills an inside ofthe cover 29 does not enter the rotor portion. Here, although the fillerflows to the winding side through the opening 32, since the windings donot rotate, this produces no ill effect.

As shown in FIGS. 3 and 4, the position detection circuit board 22 isfixed to the end surface of the motor housing 20 with bolts 34. Theneutral terminal 31 for each phase is connected to this positiondetection circuit board 22 through the wiring pattern on the wiringboard 22, and then forms the neutral point. Further, the input terminal30 of the winding for each phase extends along an axial direction from agap between the opening 32 and the position detection circuit board 22.As described later, the input terminals 30 are connected to the outputterminals of the respective power conversion circuit boards 24 and 26for each phase.

A GMR (Giant Magneto Resistance effect) element (not shown) is providedon a surface, at the sealing plate 33 side, of the position detectioncircuit board 22. The GMR element is configured to obtain magnetic poleposition information of the rotor portion in cooperation with a positiondetection permanent magnet that is fixed to a rotation shaft located atan opposite side to the output shaft portion 21. Further, a magneticshield plate 35 is provided on a surface opposite to the surface onwhich the GMR element of the position detection circuit board 22 isprovided.

This magnetic shield plate 35 has the function of suppressing aninfluence of magnetism on the GMR element, which is caused by operationof the electronic elements or components mounted on the first powerconversion circuit board 24, the first control circuit board 25, thesecond power conversion circuit board 26 and the second control circuitboard 27.

Supporting stems 36 that stand on the end surface of the motor housing20 toward an opposite side to the output shaft portion 21 in the axialdirection are formed integrally with the motor housing 20. Therefore,the supporting stem 36 is made of aluminum alloy, and its thermalconductivity is high. The supporting stems 36 are arranged at 180°angular space on opposite sides of the position detection circuit board22. As described later, the supporting stems 36 have the function of notonly fixing and supporting the heat radiation base body 23 but alsotransmitting heat from the heat radiation base body 23 to the motorhousing 20.

The supporting stems 36 are formed into a shape that thermally touchesor contacts the heat radiation base body 23 at three surfaces of thesupporting stem 36 which are a front surface and side surfaces formed atboth sides of the front surface of the supporting stem 36. Then, inorder to increase a thermal conductive area of the supporting stem 36,the side surfaces of the supporting stem 36 are shaped into an obliquesurface that obliquely extends toward an axial direction tip end. Withthis shape, a length of the side surface of the supporting stem 36 islonger, and a large thermal conductive area can be secured. On the frontsurface and a back surface of the supporting stem 36, insertion holesinto which fixing bolt is inserted are formed.

In FIGS. 3, 5 and 6, the heat radiation base body 23 is made of aluminumalloy having a good thermal conductivity, and is formed into asubstantially rectangular parallelepiped. Basically, the heat radiationbase body 23 is placed in a substantially middle on the end surface ofthe motor housing 20. In other words, the heat radiation base body 23 isdisposed on the motor housing 20 so as to pass through an area on anextension line of the rotation shaft of the rotor portion and so as toextend toward an opposite side to the output shaft portion 21 in theaxial direction. The after-mentioned electronic control boards of theredundant system are arranged in the axial direction with this heatradiation base body 23 being a center or a middle. This configuration isalso one of the outstanding features of the present embodiment.

At a lower side of each of both side surfaces 23S of the heat radiationbase body 23, a supporting stem fixing portion 38 to which thesupporting stem 36 is fixed is formed. At an upper side of each of theboth side surfaces 23S, a connector fixing portion 39 is formed. Thesupporting stem fixing portion 38 is formed into a recessed shape havinga surface that faces to the front surface of the supporting stem 36 andsurfaces that face to the respective side surfaces of the supportingstem 36. The supporting stem 36 is accommodated and fitted in thisrecessed-shaped portion. On the surface of the supporting stem fixingportion 38 which faces to the front surface of the supporting stem 36,bolt insertion holes 40 into which the fixing bolt is screwed areformed.

The surfaces of the supporting stem fixing portion 38 which face to therespective side surfaces of the supporting stem 36 are formed intooblique surfaces so as to narrow toward an upper side in line with theoblique supporting stem 36. With this shape, a large thermal conductivearea of heat transmitted from the heat radiation base body 23 toward thesupporting stem 36 can be secured. In addition, this shape can act as aguide when inserting or fitting the heat radiation base body 23 (thesupporting stem fixing portions 38) onto or to the supporting stem 36.

Further, since the side surfaces of the supporting stem 36 and thesurfaces of the supporting stem fixing portion 38 which face to theseside surfaces of the supporting stem 36 are the oblique surfaces, therespective opposing surfaces are closely fitted, then play or vibrationbetween the supporting stem 36 and the heat radiation base body 23 canbe suppressed. It is therefore possible to suppress unnecessaryvibration of the heat radiation base body 23.

The connector fixing portion 39 provided at the upper side of the heatradiation base body 23 is formed into a shape to which the power supplyconnector 28 is fitted. This will be explained using FIG. 8.

FIG. 6 shows an assembly state of the heat radiation base body 23,viewed from an opposite side to the side surface 23S of the heatradiation base body 23 shown in FIG. 5.

As shown in FIG. 6, the supporting stem fixing portions 38 of the heatradiation base body 23 is moved downward along the supporting stem 36formed at the motor housing 20. Then, when the supporting stem fixingportions 38 reaches a predetermined posit ion, the supporting stem 36and the heat radiation base body 23 are firmly fixed with the fixingbolts 41. In this state, the heat radiation base body 23 is secured onthe end surface of the motor housing 20 at the substantially middleposition on the end surface of the motor housing 20. Here, in thepresent embodiment, since a length of a fixing surface of the heatradiation base body 23 fixed to the end surface of the motor housing 20is made substantially identical to sizes of the after-mentioned controlcircuit boards 25 and 27, the heat radiation base body 23 is fixed so asto cross the middle of the end surface of the motor housing 20.

Then, with this structure, it is possible to transmit heat from theafter-mentioned electronic control boards to the heat radiation basebody 23 and further transmit heat of the heat radiation base body 23 tothe supporting stem 36. Hence, since heat from the electronic controlboards can radiate from the motor housing 20 without using theconventional ECO housing of the related art, it is possible to reducethe whole body size of the electric power steering device. Further,component count can be reduced, thereby reducing man-hour of assembly orassembly processes. Here, regarding a contact portion between thesupporting stem 36 and the heat radiation base body 23, in order toincrease thermal contact (in order to decrease an interfacial thermalresistance), a heat radiation function member such as an adhesive havinggood thermal conductivity, a heat radiation sheet and a heat radiationgrease could be interposed between the supporting stem 36 and the heatradiation base body 23.

Returning to FIG. 5, on a board fixing surface 23F corresponding to afront surface side of the heat radiation base body 23, a fixing surfacewhere the first power conversion circuit board 24 and the first controlcircuit board 25 are fixed is formed. As shown in FIGS. 3 and 8, thefirst power conversion circuit board 24 is fixed on the front surfaceside of the heat radiation base body 23, and the first control circuitboard 25 is fixed from an outer side of the first power conversioncircuit board 24.

Likewise, on a board fixing surface 23F corresponding to a back surfaceside of the heat radiation base body 23, a fixing surface where thesecond power conversion circuit board 26 and the second control circuitboard 27 are fixed is formed. As shown in FIG. 3, the second powerconversion circuit board 26 is fixed on the back surface side of theheat radiation base body 23, and the second control circuit board 27 isfixed from an outer side of the second power conversion circuit board26.

The first power conversion circuit board 24 and the second powerconversion circuit board 26 are each provided, on metal substratesthereof made of metal such as aluminium having a good thermalconductivity, with a power switching element configured from a pluralityof MOSFETs which forms a power conversion circuit and an outputconnector for output of this power switching element. Further, the firstpower conversion circuit board 24 and the second power conversioncircuit board 26 are each provided with coils forming a power supplycircuit, switching elements configured from MOSFETs, and variousconnector terminals. Since a large number of switching elements, each ofwhich carries out the switching of a large current, are mounted on thesefirst power conversion circuit board 24 and second power conversioncircuit board 26, a heat value of each of the first power conversioncircuit board 24 and the second power conversion circuit board 26 ishigh. The first power conversion circuit board 24 and the second powerconversion circuit board 26 are therefore main heat generation sources.Although heat is generated also from the first control circuit board 25and the second control circuit board 27, this heat is transmitted to theheat radiation base body 23, and radiates from the heat radiation basebody 23. This will be described later.

The metal substrates of these first power conversion circuit board 24and second power conversion circuit board 26 are fixed to accommodationrecessed portions 42 formed on the front and back surfaces of the heatradiation base body 23, as shown in FIGS. 5 and 6, with fixing bolts.The power switching element is positioned between the metal substrateand the accommodation recessed portion 42. In order to improve thermalconductive performance, a heat radiation function member such as anadhesive having good thermal conductivity, a heat radiation sheet and aheat radiation grease is interposed between the power switching elementand the accommodation recessed portion 42.

Here, needless to say, it is possible to employ a configuration in whichthe metal substrate contacts the accommodation recessed portion 42 withthe power switching element positioned at an opposite side to theaccommodation recessed portion 42. However, in the present embodiment,in order to efficiently transmit heat of the power switching element tothe heat radiation base body 23, the configuration in which the powerswitching element contacts the accommodation recessed portion 42 isemployed.

In this manner, by employing the configuration in which the first powerconversion circuit board 24 and the second power conversion circuitboard 26 are accommodated in the respective accommodation recessedportions 42 formed at the heat radiation base body 23, in the presentembodiment, the first power conversion circuit board 24 and the secondpower conversion circuit board 26 are accommodated in the heat radiationbase body 23, thereby suppressing the increase in size in the radialdirection of the electronic control unit EC.

Further, as shown in FIG. 3, the first control circuit board 25 and thesecond control circuit board 27 are fixed to the respective board fixingsurfaces 23F of the heat radiation base body 23 so as to cover the firstpower conversion circuit board 24 and the second power conversioncircuit board 26 with fixing bolts 47. That is, each of the firstcontrol circuit board 25 and the second control circuit board 27 isfixed to a fixing flat surface portion 44 that encloses theaccommodation recessed portion 42 formed on the board fixing surface 23Fof the heat radiation base body 23 with the fixing bolts 47.

A microcomputer 48 that controls the switching elements of the powerconversion circuit and its peripheral device 49 are mounted on a resinboard, made of synthetic resin etc., of each of the first controlcircuit board 25 and the second control circuit board 27. In the presentembodiment, an electrolytic capacitor 43 that forms the power supplycircuit is mounted on each of the first control circuit board 25 and thesecond control circuit board 27.

Since a body size of the electrolytic capacitor 43 is large, it isdifficult for the electrolytic capacitor 43 to be accommodated in theaccommodation recessed portion 42. Therefore, the electrolytic capacitor43 is mounted on each of the first control circuit board 25 and thesecond control circuit board 27. Since a space from the cover 29sufficiently exists as shown in FIG. 3, even though the electrolyticcapacitors 43 are arranged, this produces no ill effect.

Here, between the accommodation recessed portion 42 and the fixing flatsurface portion 44, a passage space 45 that becomes a passage when thefirst control circuit board 25 and the second control circuit board 27are fixed to the heat radiation base body 23 is formed. This passagespace 45 is formed to cool the accommodation recessed portion 42 by theair. Therefore, heat from the first control circuit board 25 and thesecond control circuit board 27 flows or is transmitted to the air inthe passage space 45, and also transmitted to the heat radiation basebody 23 through the fixing flat surface portion 44.

As shown in FIG. 5, a connector accommodation recessed portion 46 isformed on an upper end surface of the heat radiation base body 23 at anopposite side to a fixing side of the heat radiation base body 23. Thisconnector accommodation recessed portion 46 accommodates therein aninner side end of the power supply connector 28, and has the function ofmaking positioning of the power supply connector 28.

FIG. 7 is a cross section for explaining a fixing state of thesupporting stem 36 and the heat radiation base body 23. An end portionof a rotation shaft 50, which is an opposite side to the output shaftportion 21, is positioned on the end surface of the motor housing 20. Amagnet retaining member 51 is fixed to this end portion of the rotationshaft 50. The magnet retaining member 51 accommodates therein theposition detection permanent magnet 52 that forms a position detectionsensor. This position detection permanent magnet 52 is polarized so thata plurality of unit magnets are arranged annularly.

The sealing plate 33 is disposed between the position detectionpermanent magnet 52 and the position detection circuit board 22. Thissealing plate 33 is secured to the end surface of the motor housing 20,and shields a space in which the rotation shaft 50 is disposed from aspace located at the position detection circuit board 22 side. Withthis, the space in which the rotation shaft 50 is disposed can beshielded liquid-tightly or hermetically from the position detectioncircuit board 22 side space.

Therefore, water or moisture coming through the rotation shaft 50 isblocked from moving to or entering a space in which the electroniccontrol boards are arranged, thereby suppressing ill effect on theelectronic elements or components mounted on the electronic controlboards due to the water or moisture. As a matter of course, dust orparticles generated by rotation of the electric motor can be blockedfrom entering. This gives rise to an effect of preventing failure of theelectronic elements or components.

Here, a sensor that senses the water or moisture could be provided onthe position detection circuit board 22, then senses the entering of thewater or moisture. In the present embodiment, since the connectingportion is formed only at a facing surface between the motor housing 20and the cover 29, it is conceivable that the water or moisture willenter inside from this connecting portion. Since the position detectioncircuit board 22 is fixed close to the end surface of the motor housing20, if the sensor sensing the water or moisture is disposed on theposition detection circuit board 22, it is possible to sense the wateror moisture earliest.

The GMR element 53 is mounted on the surface, at the position detectionpermanent magnet 52 side, of the position detection circuit board 22,and arranged at a position facing to the position detection permanentmagnet 52. Therefore, the GMR element 53 is fixedly connected to themotor housing 20. That is, the rotation shaft 50 to which the positiondetection permanent magnet 52 is fixed is supported by the end surfaceof the motor housing 20, and the position detection circuit board 22 onwhich the GMR element 53 is mounted is also fixed to the end surface ofthe motor housing 20. Because of this, since positions of the positiondetection permanent magnet 52 and the position detection circuit board22 are determined on the end surface of the motor housing 20, accuracyof assembly of the GMR element 53 can be improved, and a precisedetection signal can be obtained.

In FIG. 7, in a state in which the supporting stem fixing portions 38 ofthe heat radiation base body 23 are moved to and fitted onto therespective supporting stems 36, the fixing bolts 41 are screwed into theheat radiation base body 23 from a radially outer side to a radiallyinner side through the supporting stems 36, and the supporting stems 36and the heat radiation base body 23 are firmly fixed with the fixingbolts 41.

This fixing direction of the fixing bolt 41 is also one of theoutstanding features of the present embodiment. In the presentembodiment, the fixing bolts 41 are screwed, into the heat radiationbase body 23 from the radially outer side to the radially inner sidethrough the supporting stems 36. With this, size reduction of the of thecontrol unit EC can be realized. As this kind of fixing manner, there isknown a fixing manner in which a fixing flange is formed at an outerperiphery of the heat radiation base body 23, and this fixing flange isfixed to an outer periphery of the motor housing 20 with fixing bolts.However, when the heat radiation base body 23 and the motor housing 20are fixed at their outer peripheral sides, the size tends to increase inthe radial direction by an amount of the fixing of the outer peripheralsides.

In contrast to this, the present embodiment utilizes the space formed bythe heat radiation base body 23 and the cover 29, and the fixing bolts41 are positioned in this space. Therefore, since the fixing bolts 41are screwed into the heat radiation base body 23 from the radially outerside to the radially inner side through the supporting stems 36, theheat radiation base body 23 and the motor housing 20 are not fixed attheir outer peripheral sides. With this, size reduction of the of thecontrol unit EC can be realized.

Further, the two supporting stems 36 at the motor housing 20 arecantilevers. Therefore, when fixing the heat radiation base body 23 andthe supporting stem 36 with the fixing bolt 41, the supporting stem 36is fixed with a slight flexure given to the supporting stem 36. Since aload in an axial direction always acts on a screw thread of the fixingbolt 41 by this slight flexure, the fixing bolt 41 can be prevented fromloosening.

After the heat radiation base body 23 is fixed to the motor housing 20,subsequently, the electronic control boards of the redundant system arefixed.

In FIG. 8, the metal substrates of the first power conversion circuitboard 24 and the second power conversion circuit board 26 are fixed tothe accommodation recessed portions 42 formed on the front and backsurfaces of the heat radiation base body 23 with fixing bolts. In thisFIG. 8, since the first control circuit board 25 and the second controlcircuit board 27 are assembled, the first power conversion circuit board24 and the second power conversion circuit board 26 are not illustrated.By employing the configuration in which the first power conversioncircuit board 24 and the second power conversion circuit board 26 areaccommodated in the respective accommodation recessed portions 42 formedat the heat radiation base body 23, in the present embodiment, the firstpower conversion circuit board 24 and the second power conversioncircuit board 26 are accommodated in the heat radiation base body 23,thereby suppressing the increase in size in the radial direction of theelectronic control unit EC.

Further, the first control circuit board 25 and the second controlcircuit board 27 are fixed to the respective board fixing surfaces 23Fof the heat radiation base body 23 so as to cover the first powerconversion circuit board 24 and the second power conversion circuitboard 26 with the fixing bolts 47. The electrolytic capacitor 43 usedfor the power supply circuit, the microcomputer 48 controlling theswitching elements of the power conversion circuit and its peripheraldevice 49 are mounted on each of the first control circuit board 25 andthe second control circuit board 27.

The power supply connector 28 is connected to the upper end surface ofthe heat radiation base body 23, and fixed at the connector fixingportions 39 shown in FIG. 5 with fixing bolts 56. The power supplyconnector 28 is connected to a vehicle-mounted battery (not shown)through a cable (not shown). Therefore, power supplied from the powersupply connector 28 is supplied to the first power conversion circuitboard 24, the first control circuit board 25, the second powerconversion circuit board 26 and the second control circuit board 27, andfurther supplied to the electric motor, then the electric motor isdriven. Subsequently, the cover 29 is fixed to the end surface of themotor housing 20 so as to seal the electronic control unit EC.

As explained above, the first power conversion circuit board 24 and thefirst control circuit board 25 are provided on the front surface of theheat radiation base body 23, and the second power conversion circuitboard 26 and the second control circuit board 27 are provided on theback surface of the heat radiation base body 23. Therefore, in thenormal condition, a part of the heat generated in an operating conditionof the first power conversion circuit board 24 and the first controlcircuit board 25 is stored (or accumulated) in the second powerconversion circuit board 26 and the second control circuit board 27through the heat radiation base body 23. It is thus possible to removethe heat of the first power conversion circuit board 24 and the firstcontrol circuit board 25 rapidly and efficiently. As a matter of course,needless to say, most of the heat, except this heat, radiates from themotor housing 20 through the heat radiation base body 23.

Further, an output terminal 54 for each phase of each of the first powerconversion circuit board 24 and the second power conversion circuitboard 26 protrudes from an upper surface of the position detectioncircuit board 22 to the radially outer side. The output terminals 54 areconnected to the input terminals 30 of the winding for the respectivephases. Since the input terminals 30 of the winding, protruding from theopenings 32, are directly connected to the output terminals 54 for therespective phases around the openings 32 without requiring complicatedwiring route in this manner, an unnecessary space for this complicatedwiring route is not required. Size reduction of the electronic controlunit EC can therefore be achieved.

Further, the neutral terminal 31 for each phase is connected to theposition detection circuit board 22 through the wiring pattern on thewiring board 22, and forms the neutral point. Likewise, for the other ofthe redundant system, the neutral terminal 31 for each phase isconnected to the position detection circuit board 22 through the wiringpattern on the wiring board 22, and forms the neutral point. Since theneutral terminals 31 of the main electronic control unit and thesub-electronic control unit for each phase are connected to the positiondetection circuit board 22 through the wiring pattern 55 on the wiringboard 22 in this manner, no complicated wiring route of the neutralterminals 31 is required, then the wiring structure is extremely simple.In addition, since complicated wiring route of the input terminals 30 tothe respective power conversion circuit boards 24 and 26 is notrequired, a space for this complicated wiring route is also notrequired. Size reduction of the electronic control unit EC can thereforebe achieved.

Furthermore, in the electronic control unit EC assembled as describedabove, in particular, a part of the heat generated in the first powerconversion circuit board 24 (or the second power-conversion circuitboard 26) is stored (or accumulated) in the second power conversioncircuit board 26 (or the first power conversion circuit board 24)through the heat radiation base body 23, and most of the heattransmitted to the heat radiation base body 23 is transmitted to themotor housing 20 through the supporting stems 36 and radiates from themotor housing 20.

In the configuration explained above, the fixing surface where the firstpower conversion circuit board 24 and the first control circuit board 25are fixed is formed on the board fixing surface 23F corresponding to thefront surface side of the heat radiation base body 23. The fixingsurface where the second power-conversion circuit board 26 and thesecond control circuit board 27 are fixed is formed on the board fixingsurface 23F corresponding to the back surface side of the heat radiationbase body 23. Then, the board fixing surface 23F corresponding to thefront surface side of the heat radiation base body 23 and the boardfixing surface 23F corresponding to the back surface side of the heatradiation base body 23 are formed so as to foe substantially parallel toeach other. Therefore, the first power conversion circuit board 24, thefirst control circuit board 25, the second power conversion circuitboard 26 and the second control circuit board 27 are also arranged to besubstantially parallel to each other.

However, it is advantageous for a heat capacity of the board thatrapidly stores (or accumulates) the heat generated in the electronicelements or components to be large in efficiently removing the heatgenerated in the electronic elements or components of the electroniccontrol unit. Further, it is advantageous for a heat capacity of theother electronic control unit (e.g. the sub-electronic control unit) tobe large in efficiently removing the heat generated in one electroniccontrol unit (e.g. the main electronic control unit). For the samereason, it is advantageous for a contacting area that contacts the heatradiation base body 23 to be large in efficiently removing the heatgenerated in the electronic control unit. From such reasons, the presentembodiment employs the following configuration. This configuration isalso one of the outstanding features of the present embodiment.

In the present embodiment, first, the first control circuit board 25 andthe second control circuit board 27 are fixed to the heat radiation basebody 23 with these boards 25 and 27 slanting or leaning with respect toa direction in which the heat radiation base body 23 extends, and aboard area of each of the first control circuit board 25 and the secondcontrol circuit board 27 is set to be large, then a large heat capacityto store (or accumulate) the heat is secured. Further, the first powerconversion circuit board 24 and the second power conversion circuitboard 26 are fixed to the heat radiation base body 23 with these boards24 and 26 slanting or leaning, and a contact area of each of the firstpower conversion circuit board 24 and the second power conversioncircuit board 26 to the heat radiation base body 23 is set to be large,then rapid removal of the heat from the first power conversion circuitboard 24 and the second power conversion circuit board 26 to the heatradiation base body 23 is secured.

In FIG. 9, the first control circuit board 25 and the second controlcircuit board 27 are fixed to the heat radiation base body 23 with theseboards 25 and 27 slanting or leaning so as to expand or broaden toward alower side with respect to an axial line of the direction in which theheat radiation base body 23 extends. When the first control circuitboard 25 and the second control circuit board 27 slant or lean in thismanner, as compared with a case where, as shown in FIG. 3, the firstcontrol circuit board 25 and the second control circuit board 27 arearranged to be substantially parallel to each other, the board area isincreased. Therefore, since additional heat storing or accumulation bythis increased board area can be made, it is possible to rapidly removethe heat generated in the electronic elements or components mounted onthe boards to the boards. Heat resistance of the electronic elements orcomponents can therefore foe improved.

Further, the first power conversion circuit board 24 and the firstcontrol circuit board 25 are provided on the front surface of the heatradiation base body 23, and the second power conversion circuit board 26and the second control circuit board 27 are provided on the back surfaceof the heat radiation base body 23. Therefore, in the normal condition,a part of the heat generated in an operating condition of the firstpower conversion circuit board 24 and the first control circuit board 25is stored (or accumulated) in the second power conversion circuit board26 and the second control circuit board 27 through the heat radiationbase body 23. It is thus possible to remove the heat of the first powerconversion circuit board 24 and the first control circuit board 25rapidly and efficiently.

Moreover, by leaning the first control circuit board 25 and the secondcontrol circuit board 27, a distance between an inner surface of thecover 29 and each of the first control circuit board 25 and the secondcontrol circuit board 27 is shortened, and the heat from the firstcontrol circuit board 25 and the second control circuit board 27 iseasily transmitted to the cover 29, thereby increasing a heat radiationamount from the cover 29.

Next, although the following configuration is not illustrated in FIG. 9,the heat radiation base body 23 could be formed into a shape that slantsor leans so as to expand or broaden toward a lower side in line with theleaning shapes of the first control circuit board 25 and the secondcontrol circuit board 27, and the first power conversion circuit board24 and the second power conversion circuit board 26 could be fixed toleaning surfaces of the heat radiation base body 23 with these boards 24and 26 leaning.

When the first power conversion circuit board 24 and the second powerconversion circuit board 26 slant or lean in this manner, as comparedwith a case where, as shown in FIG. 3, the first power conversioncircuit board 24 and the second power conversion circuit board 26 arearranged to be substantially parallel to each other, a contact area ofeach of the first power conversion circuit board 24 and the second powerconversion circuit board 26 to the heat radiation base body 23 can beincreased. Therefore, since additional rapid heat removal from the firstpower conversion circuit board 24 and the second power conversioncircuit board 26 to the heat radiation base body 23 by this increasedcontact area can be made, heat resistance of the electronic elements orcomponents can be improved.

As explained above, in the present embodiment, by fixing the board ofthe electronic control means (the electronic control unit) extendingalong the axial direction of the electric motor to the heat radiationbase body extending along the axial direction of the electric motor withthermal conduction between the board and the heat radiation base bodyallowed or secured, size reduction of the electric drive device in theradial direction can be achieved. Further, since the heat from eachboard radiates to the housing of the electric motor unit through theheat radiation base body, even though the size reduction is made, it ispossible to efficiently radiate the heat from the board to the outside.

Further, a part of the heat from the first power conversion circuitboard and the first control circuit board is stored (or accumulated) inthe second power conversion circuit board and the second control circuitboard through the heat radiation base body. It is thus possible toremove the heat of the first power conversion circuit board and thefirst control circuit board rapidly and efficiently. In addition, sincea contact area of each of the first power conversion circuit board andthe second power conversion circuit board to the heat radiation basebody is increased, it is possible to rapidly remove the heat removalfrom the first power conversion circuit board and the second powerconversion circuit board to the heat radiation base body by thisincreased contact area, thereby improving heat resistance of theelectronic elements or components.

Here, in the embodiment shown in FIG. 9, the boards slant or lean so asto expand or broaden toward the motor housing. However, needless to say,the boards could slant or lean so as to narrow toward the motor housing.In this case, conversely, opposite sides of the boards expand orbroaden.

As explained above, the present invention has the followingconfiguration. An electric drive device has: a motor housingaccommodating therein an electric motor; a heat radiation base bodyfixed to an end surface, which is an opposite side to an output shaftportion of a rotation shaft of the electric motor, of the motor housingand extending in a direction of the rotation shaft which is the oppositeside to the output shaft portion; one electronic control unit of aredundant system, the one electronic control unit arranged along adirection in which the heat radiation base body extends and having aboard that is fixed to the heat radiation base body with thermalconduction to the heat radiation base body allowed; and the otherelectronic control unit of the redundant system, the other electroniccontrol unit arranged along a direction in which the heat radiation basebody extends and having a board that is fixed to the heat radiation basebody with thermal conduction to the heat radiation base body allowedAnd, the board of the one electronic control unit and the board of theother electronic control unit are fixed to the heat radiation base bodywith the both boards slanting with respect to a direction in which theheat radiation base body extends. Then, heat radiates from the motorhousing through the heat radiation base body.

According to the configuration of the present invention, since the boardof the electronic control means (the electronic control unit) is setalong the heat radiation base body provided in the axial direction, sizereduction of the electric drive device can be achieved. Further, sincethe board of the electronic control means (the electronic control unit)of the redundant system is fixed to the heat radiation base body withthe board slanting or leaning with respect to a direction in which theheat radiation base body extends, an area of the control circuit boardcan be large, thereby rapidly storing or accumulating the heat front theelectronic elements or components to the board. Moreover, since acontact area of the board to the heat radiation base body can be large,rapid removal of the heat from the board to the heat radiation base bodyis secured.

The present invention is not limited to the above embodiment, andincludes all design modifications. The above embodiment is an embodimentthat is explained in detail to easily understand the present invention,and the present invention is not necessarily limited to the embodimenthaving all elements or components described above. Further, a part ofthe configuration of the embodiment can be replaced with a configurationof other embodiments. Also, the configuration of other embodiments couldbe added to the configuration of the embodiment. Moreover, regarding apart of the configuration of the embodiment, the configuration of otherembodiments could be added, removed and replaced.

As the electric drive device and the electric power steering devicebased on the above embodiment, for instance, the followings are raised.

That it, as one aspect of the present invention, an electric drivedevice comprises: a motor noosing accommodating therein an electricmotor that drives a mechanical control element; a heat radiation basebody fixed to an end surface, which is an opposite side to an outputshaft portion of a rotation shaft of the electric motor, of the motorhousing and extending in a direction of the rotation shaft which is theopposite side to the output shaft portion; one electronic control unitof a redundant system, the one electronic control unit arranged along adirection in which the heat radiation base body extends and having aboard that is fixed to the heat radiation base body with thermalconduction to the heat radiation base body allowed; and the otherelectronic control unit of the redundant system, the other electroniccontrol unit arranged along a direction in which the heat radiation basebody extends and having a board that is fixed to the heat radiation basebody with thermal conduction to the heat radiation base body allowedAnd, the board of the one electronic control unit and the board of theother electronic control unit are fixed to the heat radiation base bodywith the both boards slanting with respect to a direction in which theheat radiation base body extends.

As a preferable aspect of the electric drive device, the heat radiationbase body is fixed to the end surface of the motor housing at a positionclose to an area where the rotation shaft is disposed, and the oneelectronic control unit and the other electronic control unit arearranged at opposite sides of the heat radiation base body.

As another preferable aspect of the electric drive device, the heatradiation base body has fixing surfaces of the boards of the oneelectronic control unit and the other electronic control unit,accommodation recessed portions formed on the respective fixingsurfaces, and fixing flat surface portions enclosing the respectiveaccommodation recessed portions, power conversion circuit boards thatform the one and the other electronic control units are fixed to theaccommodation recessed portions with the power conversion circuit boardsslanting, and control circuit boards that form the one and the otherelectronic control units are fixed to the fixing flat surface portionsso as to cover the respective power conversion circuit boards.

As another preferable aspect of the electric drive device, the heatradiation base body has fixing surfaces of the boards of the oneelectronic control unit and the other electronic control unit,accommodation recessed portions formed on the respective fixingsurfaces, and fixing flat surface portions enclosing the respectiveaccommodation recessed portions, power conversion circuit boards thatform the one and the other electronic control units are fixed to theaccommodation recessed portions with the power conversion circuit boardsslanting, and control circuit boards that form the one and the otherelectronic control units are fixed to the fixing flat surface portionswith the control circuit boards slanting so as to cover the respectivepower conversion circuit boards.

As another preferable aspect of the electric drive device, a positiondetection circuit board that detects a rotation position of a rotor ofthe electric motor is fixed to the end surface of the motor housing,supporting stems that support the heat radiation base body are formedintegrally with the end surface of the motor housing and arranged atopposite sides of the position detection circuit board, and the heatradiation base body is fixed to the supporting stems.

As another preferable aspect of the electric drive device, a powerconversion circuit and a power supply circuit except an electrolyticcapacitor are mounted on the power conversion circuit boards forming theone and the other electronic control units, and a microcomputer thatcontrols the power conversion circuit, a peripheral device and theelectrolytic capacitor of the power supply circuit are mounted on thecontrol circuit boards forming the one and the other electronic controlunits.

From the other view point, an electric power steering device comprises:an electric motor providing a steering assistive force to a steeringshaft on the basis of an output from a torque sensor that detects aturning direction and a turning torque of the steering shaft; a motorhousing accommodating therein the electric motor; a heat radiation basebody fixed to an end surface, which is an opposite side to an outputshaft portion of a rotation shaft of the electric motor, of the motorhousing and extending in a direction of the rotation shaft which is theopposite side to the output shaft portion; one electronic control unitof a redundant system, the one electronic control unit arranged along adirection in which the heat radiation base body extends and having aboard that is fixed to the heat radiation base body with thermalconduction to the heat radiation base body allowed; and the otherelectronic control unit of the redundant system, the other electroniccontrol unit arranged along a direction in which the heat radiation basebody extends and having a board that is fixed to the heat radiation basebody with thermal conduction to the heat radiation base body allowedAnd, the board of the one electronic control unit and the board of theother electronic control unit are fixed to the heat radiation base bodywith the both boards slanting with respect to a direction in which theheat radiation base body extends.

As a preferable aspect of the electric power steering device, the heatradiation base body is fixed to the end surface of the motor housing ata position close to an area where the rotation shaft is disposed, andthe one electronic control unit and the other electronic control unitare arranged at opposite sides of the heat radiation base body.

As another preferable aspect of the electric power steering device, theheat radiation base body has fixing surfaces of the boards of the oneelectronic control unit and the other electronic control unit,accommodation recessed portions formed on the respective fixingsurfaces, and fixing flat surface portions enclosing the respectiveaccommodation recessed portions, power conversion circuit boards thatform the one and the other electronic control units are fixed to theaccommodation recessed portions with the power conversion circuit boardsslanting, and control circuit boards that form the one and the otherelectronic control units are fixed to the fixing flat surface portionsso as to cover the respective power conversion circuit boards.

As another preferable aspect of the electric power steering device, theheat radiation base body has fixing surfaces of the boards of the oneelectronic control unit and the other electronic control unit,accommodation recessed portions formed on the respective fixingsurfaces, and fixing flat surface portions enclosing the respectiveaccommodation recessed portions, power conversion circuit boards thatform the one and the other electronic control units are fixed to theaccommodation recessed portions with the power conversion circuit boardsslanting, and control circuit boards that form the one and the otherelectronic control units are fixed to the fixing flat surface portionswith the control circuit boards slanting so as to cover the respectivepower conversion circuit boards.

As another preferable aspect of the electric power steering device, aposition detection circuit board that detects a rotation position of arotor of the electric motor is fixed to the end surface of the motorhousing, supporting stems that support the heat radiation base body areformed integrally with the end surface of the motor housing and arrangedat opposite sides of the position detection circuit board, and the heatradiation base body is fixed to the supporting stems.

As another preferable aspect of the electric power steering device, apower conversion circuit and a power supply circuit except anelectrolytic capacitor are mounted on the power conversion circuitboards forming the one and the other electronic control units, and amicrocomputer that controls the power conversion circuit, a peripheraldevice and the electrolytic capacitor of the power supply circuit aremounted on the control circuit boards forming the one and the otherelectronic control units.

The invention claimed is:
 1. An electric drive device comprising: amotor housing accommodating therein an electric motor that drives amechanical control element; a heat radiation base body fixed to an endsurface, which is an opposite side to an output shaft portion of arotation shaft of the electric motor, of the motor housing and extendingin a direction of the rotation shaft which is the opposite side to theoutput shaft portion; one electronic control unit of a redundant system,the one electronic control unit arranged along a direction in which theheat radiation base body extends and fixed to the heat radiation basebody with thermal conduction to the heat radiation base body allowed,and the one electronic control unit having a board that mounts thereonat least a microcomputer and having a power switching element thatdrives and controls the electric motor; and the other electronic controlunit of the redundant system, the other electronic control unit arrangedalong a direction in which the heat radiation base body extends andfixed to the heat radiation base body with thermal conduction to theheat radiation base body allowed, and the other electronic control unithaving a board that mounts thereon at least a microcomputer and having apower switching element that drives and controls the electric motor, andthe board of the one electronic control unit and the board of the otherelectronic control unit being fixed to the heat radiation base body withthe both boards slanting with respect to a direction in which the heatradiation base body extends.
 2. The electric drive device as claimed inclaim 1, wherein: the heat radiation base body is fixed to the endsurface of the motor housing at a position close to an area where therotation shaft is disposed, and the board of the one electronic controlunit and the board of the other electronic control unit are arranged atopposite sides of the heat radiation base body.
 3. The electric drivedevice as claimed in claim 2, wherein: the heat radiation base body hasfixing surfaces of the boards of the one electronic control unit and theother electronic control unit, accommodation recessed portions formed onthe respective fixing surfaces, and fixing flat surface portionsenclosing the respective accommodation recessed portions, powerconversion circuits that form the one and the other electronic controlunits and have the power switching elements are fixed to theaccommodation recessed portions with the power conversion circuitsslanting, and the boards of the one and the other electronic controlunits are fixed to the fixing flat surface portions so as to cover therespective power conversion circuits.
 4. The electric drive device asclaimed in claim 3, wherein: the power conversion circuits forming theone and the other electronic control units are boards on which a powerconversion circuit and a power supply circuit except an electrolyticcapacitor are mounted, and the microcomputer that controls the powerconversion circuit, a peripheral device and the electrolytic capacitorof the power supply circuit are mounted on the boards forming the oneand the other electronic control units.
 5. The electric drive device asclaimed in claim 3, wherein: a position detection circuit board thatdetects a rotation position of a rotor of the electric motor is fixed tothe end surface of the motor housing, supporting stems that support theheat radiation base body are formed integrally with the end surface ofthe motor housing and arranged at opposite sides of the positiondetection circuit board, and the heat radiation base body is fixed tothe supporting stems.
 6. The electric drive device as claimed in claim2, wherein: the heat radiation base body has fixing surfaces of theboards of the one electronic control unit and the other electroniccontrol unit, accommodation recessed portions formed on the respectivefixing surfaces, and fixing flat surface portions enclosing therespective accommodation recessed portions, power conversion circuitshaving the power switching elements that form the one and the otherelectronic control units are fixed parallel to the accommodationrecessed portions, and the boards of the one and the other electroniccontrol units are fixed to the fixing flat surface portions with theboards slanting so as to cover the respective power conversion circuits.7. An electric power steering device comprising: an electric motorproviding a steering assistive force to a steering shaft on the basis ofan output from a torque sensor that detects a turning direction and aturning torque of the steering shaft; a motor housing accommodatingtherein the electric motor; a heat radiation base body fixed to an endsurface, which is an opposite side to an output shaft portion of arotation shaft of the electric motor, of the motor housing and extendingin a direction of the rotation shaft which is the opposite side to theoutput shaft portion; one electronic control unit of a redundant system,the one electronic control unit arranged along a direction in which theheat radiation base body extends and fixed to the heat radiation basebody with thermal conduction to the heat radiation base body allowed,and the one electronic control unit having a board that mounts thereonat least a microcomputer and having a power switching element thatdrives and controls the electric motor; and the other electronic controlunit of the redundant system, the other electronic control unit arrangedalong a direction in which the heat radiation base body extends andfixed to the heat radiation base body with thermal conduction to theheat radiation base body allowed, and the other electronic control unithaving a board that mounts thereon at least a microcomputer and having apower switching element that drives and controls the electric motor, andthe board of the one electronic control unit and the board of the otherelectronic control unit being fixed to the heat radiation base body withthe both boards slanting with respect to a direction in which the heatradiation base body extends.
 8. The electric power steering device asclaimed in claim 7, wherein: the heat radiation base body is fixed tothe end surface of the motor housing at a position close to an areawhere the rotation shaft is disposed, and the board of the oneelectronic control unit and the board of the other electronic controlunit are arranged at opposite sides of the heat radiation base body. 9.The electric power steering device as claimed in claim 8, wherein: theheat radiation base body has fixing surfaces of the boards of the oneelectronic control unit and the other electronic control unit,accommodation recessed portions formed on the respective fixingsurfaces, and fixing flat surface portions enclosing the respectiveaccommodation recessed portions, power conversion circuits that form theone and the other electronic control units and have the power switchingelements are fixed to the accommodation recessed portions with the powerconversion circuits slanting, and the boards of the one and the otherelectronic control units are fixed to the fixing flat surface portionsso as to cover the respective power conversion circuits.
 10. Theelectric power steering device as claimed in claim 9, wherein: the powerconversion circuits forming the one and the other electronic controlunits are boards on which a power conversion circuit and a power supplycircuit except an electrolytic capacitor are mounted, and themicrocomputer that controls the power conversion circuit, a peripheraldevice and the electrolytic capacitor of the power supply circuit aremounted on the boards forming the one and the other electronic controlunits.
 11. The electric power steering device as claimed in claim 9,wherein: a position detection circuit board that detects a rotationposition of a rotor of the electric motor is fixed to the end surface ofthe motor housing, supporting stems that support the heat radiation basebody are formed integrally with the end surface of the motor housing andarranged at opposite sides of the position detection circuit board, andthe heat radiation base body is fixed to the supporting stems.
 12. Theelectric power steering device as claimed in claim 8, wherein: the heatradiation base body has fixing surfaces of the boards of the oneelectronic control unit and the other electronic control unit,accommodation recessed portions formed on the respective fixingsurfaces, and fixing flat surface portions enclosing the respectiveaccommodation recessed portions, power conversion circuits having thepower switching elements that form the one and the other electroniccontrol units are fixed parallel to the accommodation recessed portions,and the boards of the one and the other electronic control units arefixed to the fixing flat surface portions with the boards slanting so asto cover the respective power conversion circuits.